In many applications, for instance in many applications employing microcontrollers, there is a need for highly reliable memory devices, in particular non-volatile memory devices. In the automotive sector, for example, the need for such memory systems is constantly rising since modern vehicles comprise an increasing number of microcontrollers. These microcontrollers are used for such diverse purposes as engine and transmission control, advanced driver assistance systems, or infotainment systems. All these applications require memory to function. Since many of these applications relate to aspects relevant to safety, highly reliable memory is needed. Furthermore, such high quality memory systems not only need to function well under normal conditions, but should also be robust in the occurrence of faults.
A conventional memory device comprises a plurality of memory cells. In a non-volatile memory device these memory cells are non-volatile memory cells. In a Flash memory, for example, each of these non-volatile memory cells comprises a floating-gate transistor. A floating-gate transistor comprises a floating-gate which is electrically isolated from the other components of the floating-gate transistor. This floating-gate can therefore be used to store a charge for long periods of time. The amount of charge stored in a floating-gate is usually modified by mechanisms such as Fowler-Nordheim tunneling or hot-carrier injection. Modifying the amount of charge stored in a floating-gate therefore requires applying specific voltages to the terminals of the floating-gate transistor, i.e. to the drain, source, control gate, and bulk of the floating-gate transistor.
In addition to the floating-gate transistors, a Flash memory usually comprises a plurality of additional transistors. In particular, each memory cell may comprise an additional transistor which may be employed for selecting the respective memory cell for erasing, programming, or reading. Further additional transistors may be provided at specific positions in the memory array for performing specific tasks such as selecting certain sets of memory cells for erasing, programming, or reading. As a consequence, a Flash memory comprises a plurality of transistors, the terminals of which need to be provided with specific voltages in order to allow the transistors to function properly.
In a conventional non-volatile memory device the non-volatile memory cells are arranged in a regular grid, i.e. the memory cells are arranged in rows and columns. This arrangement allows for a simple management of the voltage supply lines required for providing each memory cell with the voltages needed for its operation. A conventional Flash memory may comprise a plurality of horizontal voltage supply lines coupled to the control gates of a row of floating-gate transistors. These horizontal voltage supply lines are generally referred to as word lines and the set of non-volatile memory cells coupled to a single word line is generally referred to as a page. A conventional Flash memory furthermore may comprise a plurality of vertical voltage supply lines coupled to drain terminals of a column of floating-gate transistors. These vertical voltage supply lines are generally referred to as bit lines. A conventional Flash memory may comprise additional voltage supply lines such as source lines or select lines.
A conventional Flash memory furthermore comprises voltage supply sources which are employed to provide the voltages required for operation of the Flash memory. These voltage supply sources are typically implemented as charge pumps.
Since non-volatile memories such as Flash memories are semiconductor devices exhibiting a large quantity of microscopic structures, single faults in the array of memory cells for example evolving only during the operation of the chip cannot always be avoided. A defect in a memory array may, however, result in a low resistive path on a high ohmic terminal which can lead to a catastrophic failure of a complete memory array. In particular, if the non-volatile memory device comprises voltage supply sources, such a low resistive path may result in erroneous voltages being supplied to the memory array.
For these or other reasons there is a need for an improved system and/or method for providing voltage supply protection in a memory device.